1. Field of the Invention
The present invention relates to an image forming apparatus that employs a developing agent.
2. Description of the Related Art
Developing agents are employed in electrophotographic image forming apparatus including printers, copiers, and facsimile machines. A typical apparatus of this type has a photosensitive drum that functions as an image carrier, a developer roller that applies a developing agent known as toner to develop an electrostatic latent image formed on the photosensitive drum, a toner supply roller with a porous surface that supplies toner to the developer roller, and an agitator or the like, disposed upwardly adjacent the toner supply roller, that stirs the toner to maintain a continuous flow of toner to the toner supply roller. A color image forming apparatus may have a plurality of these image forming units with toners of different colors.
Japanese Patent Application Publication No. 2005-172842 describes a type of agitator that revolves in a circular orbit, making periodic contact with the toner supply roller, to prevent a loss of fluidity of the toner in the vicinity of the toner supply roller due to the ‘nip’ between the developer roller and toner supply roller. At high printing speeds, however, even this type of agitator may fail to maintain a steady toner flow. The problem is that the rapidly revolving agitator flings toner away from it, so that after a while the agitator is revolving in a hollow space surrounded by compacted layers of toner banked against the walls of the toner container. As a result, the toner supply roller fails to receive an adequate supply of toner and printing becomes faint.